This invention is related to the field of pumps. More particularly, this invention is related to the field of dry-pit submersible pumps.
Broadly speaking, pumps can be classified into two types: dry and submersible. Submersible pumps are used where both the pump and motor must be placed in the water to be pumped. In deep wells, for instance, it is necessary to locate the pump and motor at the bottom of the well and "push" water up because it is not possible to pull water up from a depth greater than approximately 30 feet. While motors for submersible pumps can be made rather compact because of the efficient cooling provided by the surrounding water, they are relatively expensive to manufacture and therefore only used where absolutely necessary.
Dry pumps, in contrast to submersibles, have motors designed to operate in air, and are used wherever the motor is not subject to being immersed in water. Because air is a much less effective cooling medium, motors for dry pumps are typically equipped with a fan mounted to the drive shaft to generate a stream of cooling air over the outside of the motor. A particularly common type of motor used to power dry pumps is known as a totally-enclosed, fan-cooled, or TEFC, motor. In a TEFC motor, the casing forms a sealed container around the motor armature to seal against contamination. As a result of this sealing, TEFC motors are substantially waterproof, and may even be submerged for short periods of time while idle. However, if a TEFC motor is operated under water, the cooling fan would generate so much increased drag relative to operation in air that the motor would become overloaded and burn out. Thus, existing TEFC motors have not been suitable for operation, even temporarily, under water.
In some pump applications, the pump is normally expected to operate in air, but may under some circumstances become immersed for periods of time. This may occur, for instance, where a pumping station is inundated during a flood, or a sump pump fails to keep up with influx to a sump pit. In many cases, it is important that the pump continues to operate in the event of submersion. In such cases, a submersible pump/motor combination has been used and simply operated in air under normal circumstances. However, because the air cannot cool the motor as effectively as water, some additional provision must be made to cool the motor. For instance, the motor may be oversized and run at less than rated capacity to thereby provide additional surface area to enhance cooling. In some cases a cooling jacket is used to circulate pumpage or oil around the motor. Unfortunately, these systems for cooling add significantly to the expense of a motor that is already more expensive than a comparable TEFC motor. By way of example, a submersible pump/motor combination designed to operate in air may be more than three times as expensive as a comparable dry system. Another disadvantage of these solutions is that a submersible motor must be directly connected to the pump and can not be connected through an intermediate frame as is known in the art.
Previous attempts to cool a submersible pump/motor combination operating in air have included installing a cooling fan separate from the motor. A shroud extends around the fan and the motor to direct the air over the motor. This solution can significantly add to the setup requirements and expense of the pump. In addition, this solution may not be physically practical in some pumping applications.
It is therefore an object of the present invention to provide an economical pump/motor system for use in an environment that may be subject to periodic immersion.
It is a further object of this invention to provide such a system which can make use of existing TEFC motor designs.
More generally, it is an object of the present invention to provide a fan-cooled electric motor that will not be overloaded by drag from the fan when operated underwater.
The difficulties and problems found in past dry-pit submersible pumps are overcome by using a modified TEFC electric motor to power the pump and by providing a release mechanism to prevent the fan from creating excessive drag when submerged in water. Air from the fan cools the motor when the water level is below the motor, and the surrounding water cools the motor when the water level rises to at least partially surround the motor. When the fan is at least partially submerged, the release mechanism prevents the fan from imposing an excess load on the motor due to the surrounding water.